The following patent publications are believed to represent the current state of the art:
U.S. Pat. Nos. 6,945,354; 6,739,822; 6,675,920; 6,751,588; 6,600,992; 6,405,975; 6,390,762; 6,357,989; 6,352,130; 6,305,484; 6,283,696; 6,209,671; 5,860,785; 5,680,125; 5,655,733; 5,562,388; 5,549,436; 5,516,252; 5,511,926; 5,480,274; 5,381,987; 5,346,354; 5,314,287; 5,308,212; 5,302,076; 5,302,075; 5,302,074; 5,261,778; 5,259,572; 5,219,033; 5,202,075; 5,176,341; 5,151,003; 5,110,067; 5,082,082; 5,078,340; 5,054,714; 5,051,052; 5,048,625; 5,013,205; 4,997,331; 4,976,499; 4,950,121; 4,923,253; 4,917,564; 4,917,563; 4,913,253; 4,911,604; 4,911,603; 4,836,734; 4,810,157; 4,745,410; 4,730,685; 4,658,924; 4,632,625; 4,482,961; 4,375,244; 4,225,279; 4,113,041 and 4,007,890;
U.S. Patent Publication Number 2003/095854;
PCT Patent Publication Numbers WO 93/13985; WO 89/03343 and WO 98/52822; and
Patent publication numbers RU 2302980; RU 2271316; EP 1623924; EP 1190947; JP 2279497; JP 4138997; JP 57070741; JP 56002237; GB 1249465; DE 3844744; DE 4446048; DE 4446047; DE 4131649; DE 4102861; DE 4009419; DE 4007610; DE 19734238; DE 3534045; DE 3521429; DE 3327629; DE 3327628; DE 4340919; FR 2581965 and FR 2675919.